Ar Ciela, also referred to as the "language of the planet", is not a language conceived of for human use. Rather, it is a language that expresses the will of the planet and describes things like natural phenomena (in terms applicable to Earth, examples would be weather systems, volcanic activity, tectonic shifts, and other properties that govern the natural cycle of life). Taken in this context, Ar ciela can be viewed as the language used by Ar ciel to manifest change.

The full range of Ar ciela phonology cannot be perceived by human ears. This does not seem unreasonable when considering the scale on which the language, which is conveyed as pure dynamic H-waves, operates, as a force that shapes the world. The full spectrum of Ar ciela spans 20-600,000Hz; compared to the human-perceptible domain of 20-20,000Hz, the upper bound of Ar ciela's frequency range is thirty times higher. Were this range to be recorded, instruments capable of sampling at a rate of 1,200kHz would be required (for reference, CD-quality audio is sampled at 44.1kHz).

So, then, what does Ar ciela sound like when observed by human ears? One method of approximating the difference between the full range of Ar ciela and what humans can hear is as follows: take a recording of speech or song and load it into a waveform editor, then resample it at 100Hz, one twentieth of what human ears can perceive. Play back the result and you will find the audio muffled and hard to understand. Perceived by humans, Ar ciela is much like the 100Hz sample of the original audio.

A 4000Hz example is available in Vorbis format. 4000Hz was chosen because it's the smallest sampling rate known to work with most sound cards, though it only demonstrates 1/10 range-compression, rather than the target 1/40; just imagine that the quality would be much worse. Download: 44100Hz, 4000Hz.

Suppose the word recorded were [okaasan] (おかあさん : mother). Had you resampled it at 100Hz, effectively cutting off every frequency higher than that value, you would have been left with something that sounds like /ohoohon/ (おほおほん), which has no meaning. However, phonologically, the utterance still has significance: it retains five morae (including the nasal), emphasis is placed over the second and third morae, and the prosodical pattern holds. Despite the phonological similarities, though, what was [okaasan] may be mentally interpreted as the equally meaningless /notaahau/ (のたあはう), since /ohoohon/ isn't any more recognizable as a word.

Expanding on the presented idea, consider the Ar ciela utterance transcribed as "Tisia": not knowing what its full enunciation sounds like, it is impossible to know exactly what word it really is. Were you able to hear it pronounced at 600,000Hz, however, it would be possible to indentify, with confidence, the true form of the word being uttered.

An everyday example of the significance of frequency ranges is in how a Japanese speaker deals with the English words "grass" and "glass". Since Japanese phonemes do not distinguish between the high frequencies that contrast /l/ and /r/ in English, native speakers cannot, without great effort, mentally hear the difference between the words: to them, both are /gurasu/ (グラース).

A visual look at the subset of human-audible sound relative to the full frequency range of Ar ciela.
It is impossible to observe the full range of sound because of limitations on what can be heard.

Because the true form of Ar ciela utterances cannot be aurally perceived by humans, its depictions are presented in three-dimensional terms, as a logical matrix that can be used to construct visual forms. All renditions describe the same Ar ciela language.

Ar ciela is transcribed using two notation layers, described below.

Public notation uses a set of 26 symbols, each representing a sound in the human-audible domain. Because this notation is limited to the human-audible domain, it cannot be used to fully model all of Ar ciela, providing a simple, though highly lossy, encoding scheme.

The Ar ciela compartment font's standard form is that of Public Ar ciela.

Compartment notation is an extension of Public notation, in which annotations are added to the set of 26 symbols, describing properties of the sound that fall outside of the human-audible domain. They provide additional dimensions to complete the aforementioned logical matrix.

When casually observing Ar ciela, it is impossible for humans to determine which Compartment notation elements to use for transcription, since they describe inaudible properties of the sounds. Even if the full range of sound could be heard, though, the listener would need to be trained to recognize the differences between Compartment notation elements for each sound. However, despite the complications associated with observation, Compartment notation is necessary to properly analyse transcribed Ar ciela.

The extensions provided by Compartment notation are thus: markings that sub-divide the Public symbols into five frequency categories and four amplitude categories. These sub-divided categories are collectively referred to as Compartments.

The use of Compartment notation is not unlike that of diacritics, where an umlaut (¨) can, in languages such as German, fundamentally change the pronunciation of a word.

Compartment notation provides approximately logarithmic sub-division of the frequency range from 20,000Hz through 600,000Hz. To effect this sub-division, notations describe two properties: FMCL (frequency) and AMCL (amplitude).

FMCL notation applies to sounds with a frequency over 20,000Hz, providing five distinct categories. For example, using the 100Hz example from before, what is heard as [a] (あ) may have actually been [ka] (か) or [sa] (さ); [ka] and [sa] are distinguishable only at frequencies higher than 100Hz.

AMCL describes pronunciation properties within frequency categories. For example, in the 20,000Hz range, with the sounds [ka] (か) and [sa] (さ), the frequency-distribution is such that the former has a short, sharp leading burst, while the latter is characterised by a softer, more rolling pattern.

Notes:

• When written, FMCL annotation is placed in the upper section of an otherwise-Public character, with AMCL annotation appearing on the lower side.
• Compartment notation is not used with vowels, since morae are not subject to variances in enunciation: their formants remain steady throughout the duration of the sound.

"Ec Tisia" means 「empathy + growth」 and 「everyone + sincerity + forgiveness + hope + belief」, the sum of the symbols that comprise its words; its Compartment form is "Ec[s-4/half] T[s-3/quad]is[s-4/dual]ia", which is rendered in glyphs above.

Ar ciela is the basis of the Risshizen Tsukuyomi language, used by the Tsukikanade. Like Risshizen Tsukuyomi, each uttered sound has its own associated meaning (expressible as feelings through H-waves). As each word is a collection of sounds, each carrying its own meaning, the symbolism of a complete word is that of the aggregated sum of its sounds: for example, "Ec Tisia" literally means 「empathy + growth」 and 「everyone + sincerity + forgiveness + hope + belief」, which is collectively transmitted via H-waves, as a unified message along the lines of "everything is forgiven".

Note that the effective meaning of the message is not necessarily a one-to-one match with its constituent sounds. Since each symbol that makes up a word in Ar ciela describes a single feeling, the language can be viewed as being similar to Emotion Sounds in Hymmnos.

Vowels are not sub-divided by waveform category, for reasons described in the preceding section; rather, they work with associated consonants to form meaning. The vowels' meaning, of which there are many possibilities, is selected based on its context. A generalised category is presented in square brackets, though it is purely an arbitrary human choice.

Specific references (such as to a planet's language (Ar ciela) as a concrete noun) are not possible. Because Ar ciela is a means of conveying composite feelings, a word that describes "A" would need to contain "U" or "N" and would therefore no longer describe the purity of the feeling associated with "A". Expressing concrete concepts like arbitrary words with the abstract feelings afforded by vowels and consonants cannot be done.

The following table maps each Ar ciela sound to its associated feelings.

Ar cia laboratory research

• This table is incomplete: at this time, only identified feelings have been recorded
• The assignment of I-IX is done by the laboratory; it is an arbitrary process not endemic to Ar ciela
• It would be possible to further sub-divide a section (III, for example) into ten new sections and still have more than enough feelings to fill the slots.

(Editor's note: No, it's not clear what the I-IX stuff actually means at this time)